Greywacke slate and quartzite 27 Upper conglomerate 27 Arkose 28 Structural features and disturbances 28 Relations to other formations 29 Origin and correlation 31 6. Post-Huronian eruptives 32 Quartz diabase 32 Character of intrusion and distribution relative to older systems 32 Macroscopic character 33 Microscopic character 34 Local description 36 Age 37 Olivine diabase 38 7. Pleistocene 38 V. Economic Geology 40 1. Silver 40 Distribution 40 Surface indications 40 Structure of veins 41 Composition of veins 41 Local description 42 Future possibilities 44 2. Copper 45 3. Iron ores 45 Hematite 45 Magnetite 46 4. Asbestos 46 Distribution 46 Origin 47 ILLUSTRATIONS. 1. Frontispiece—View at Foot of Duncan Lake 5 2. Diagram illustrating the structure of large hills 12 3. Diagram illustrating geological relationships 16 4. View looking north from middle of Duncan Lake, 550 ft. hill in distance 20 5. West Branch Montreal River, near Mosher Lake 22 6. Fifth portage on West Branch of Montreal River, showing Huronian slate 30 7. Inclined Huronian Beds, Duncan Lake 32 R. W. BROCK, Esq., Director Geological Survey Branch, Department of Mines.